Various abbreviations are used throughout this application and for ease of reference those most frequently used are set out below:                EMG—electromyogram        ECG—electrocardiogram        COPD—chronic obstructive pulmonary disease        AECOPD—acute exacerbation of COPD        HR—Heart Rate        NRD—neural respiratory drive        NRDI—neural respiratory drive index        NRDTP—neural respiratory drive time product        NRDTI—neural respiratory drive time index        RR—respiratory rate        RMS—root mean square        
The use of physiological biomarkers to monitor and track clinical change in patients in both acute care organisations and in the community is an area of increasing interest to health care providers. Early detection of clinical deterioration and assessing the response to treatment correspond to improved clinical outcomes in patients. Despite the rationale for this approach, there is little published evidence to support the use of the current basic physiological monitoring systems available for detection of deterioration in patients as being sufficiently sensitive or having sufficient specificity for early detection (Hillman et al. (2005) Lancet 365, 2091-7).
Whilst heart rate (HR) and respiratory rate (RR) are commonly used clinical physiological variables in acute care, measurements of neural respiratory drive (NRD) and neural respiratory drive index (NRDI) are advanced physiological biomarkers that have been shown to have greater sensitivity and specificity in assessing the intensity, timing and duration of respiratory effort, which is defined by the balance between respiratory muscle load and capacity (Duiverman et al. (2004) J. Appl. Physiol. 96, 1723-9; Jolley et al. (2009) Eur. Respir. J. 33, 289-97; Steier et al. (2009) Thorax 64; 719-25).
Whilst this technique is an established research technique (Jolley et al. (2009); Steier et al. (2011) Thorax 66, 609-614; Murphy et al. (2011) Thorax 66, 602-8, incorporated herein by reference in its entirety), the limitations set out above have prevented it from becoming useful as a clinical tool. Indeed, the time involved in undertaking the analysis has limited its applicability to research situations. Whilst generic devices exist to perform the first steps of the process there is no known system available in clinical use to display NRD and NRDI as a physiological biomarker. One system utilises surface electrodes to measure EMG activity (Duiverman et al. (2004)), however, the commercial device has not been robust or reliable enough to move from the research to the clinical arena. Furthermore, the processing of the signal displays a log ratio of the EMG activity, which has no clinical advantage. In addition, this method has not focussed on an approach of normalisation of the EMGpara signal to the maximal EMGpara signal manoeuvre. These factors have prevented it from becoming a useful clinical tool.